I have done quite a bit more testing with my Sierra Wireless AirCard 880 on Ubuntu, both the current 8.04.1 (Hardy Heron) and the Alpha 5 release of 8.10 (Intrepid Ibex). The results are very pleasing and very encouraging.
As I said yesterday, on 8.04 the AirCard works with wvdial just fine, once the config file has been filled in appropriately. I tested it on the Speakeasy Speed Test and it reported 2+ Mbps download and 256 Kbps upload. As far as I can tell, however, it does not work with the Network Manager on 8.04. It looks like it might be possible to configure it as a Point-to-Point network connection, but I could not figure out any way to get that working.
On 8.10 Alpha 5, things got really interesting. First, of course, it still works just fine with wvdial, using the same configuration as on 8.04 - no surprise. But then I noticed that it looks like they are doing a lot of work on the Network Manager for 8.10, and there is a new tab for "Mobile Broadband" connection. Of course, I haven't learned my lesson about Ubuntu (and Linux in general) yet, although I have said it here myself many times already - don't overcomplicate things! I tried entering various parts of the configuration info in the Mobile Broadband device, and it wouldn't connect. I finally gave up and decided to wait to see if it is any better in the next Alpha, Beta or the final release. I continued using it with wvdial, until once when I was looking at the Network Manager again, and I idly clicked ont he Mobile Broadband connection, fully expecting it to say "Disconnected" - especially since I had done NOTHING to try to configure it. To my utter surprise, it connected! Hmmmm.
Further investigation shows that the problem is with initialization. When the card is first inserted after Ubuntu starts up, it will not connect through the Network Manager / Mobile Broadband device until the card has been initialized, for example by running the wvdial script once. After that has been done, you can then connect and disconnect through Network Manager as much as you like, and it works just great!
As I said, this is for me personally extremely good news, because it means I won't have to shut down Ubuntu and boot Windows to get Internet access during my commute.